First week euphoria is the term used to describe the feelings of elation you experience during the first week of giving up something you are addicted to. You feel happier and more confident during the first seven days, before 'hitting the wall' on the eighth day and probably giving up trying.

James (8th January, 2009): Still given up the booze?
Jonas: Nupe, didn't make it past first week euphoria, I'm on the piss tonight!